Submarine: Map

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A submarine is a watercraft capable of
independent operation below the surface of the water. It differs
from a submersible, which has only
limited underwater capability. The term submarine most commonly
refers to large crewed autonomous vessels; however, historically or
more casually, submarine can also refer to medium sized or smaller
vessels (midget submarines,
wet subs), Remotely Operated Vehicles or
robots. The word
submarine was originally an adjective meaning "under the sea", and
so consequently other uses such as "submarine engineering" or
"submarine cable" may
not actually refer to submarines at all. Submarine was shortened
from the term "submarine boat", and is often further shortened to
"sub".

Submarines are referred to as "boats" for
historical reasons because vessels deployed from a ship are
referred to as boats. The first submarines were launched in such a
manner. The English
term U-boat for a German submarine
comes from the German word for
submarine, U-Boot, itself an abbreviation for
Unterseeboot ("undersea
boat").

Although experimental submarines had been built before, submarine
design took off during the 19th century. Submarines were first
widely used in World War I, and feature
in many large navies. Military usage ranges
from attacking enemy ships or submarines, aircraft carrier protection, blockade running, ballistic missile submarines as
part of a nuclear strike force, reconnaissance, conventional land attack (for
example using a cruise missile), and
covert insertion of special forces.
Civilian uses for submarines include marine science, salvage, exploration and
facility inspection/maintenance. Submarines can also be specialized
to a function such as search and rescue, or undersea cable repair.
Submarines are also used in tourism and for academic
research.

Submarines
have one of the largest ranges of capabilities in any vessel,
ranging from small autonomous examples to one or two-person vessels
operating for a few hours, to vessels which can remain submerged
for 6 months such as the RussianTyphoon class. Submarines can
work at greater depths than are survivable or practical for human
divers. Modern deep diving submarines are
derived from the bathyscaphe, which in
turn was an evolution of the diving
bell.

Most large submarines comprise a cylindrical body with
hemispherical (and/or conical) ends and a vertical structure,
usually located amidships, which houses communications and sensing
devices as well as periscopes. In modern submarines this structure
is the "sail" in American usage ("fin" in European usage). A
"conning tower" was a feature of
earlier designs: a separate pressure hull above the main body of
the boat that allowed the use of shorter periscopes. There is a
propeller (or pump jet) at the rear and various hydrodynamic
control fins as well as ballast tanks. Smaller, deep diving and
specialty submarines may deviate significantly from this
traditional layout.

Before and during World War II, the
primary role of the submarine was anti-surface ship warfare.
Submarines would attack either on the surface or submerged, using
torpedoes or (on the surface) deck guns.
They were particularly effective in sinking Allied transatlantic
shipping in both World Wars, and in disrupting Japanese supply
routes and naval operations in the Pacific in World War II.

Mine-laying submarines were developed in
the early part of the 20th century. The facility was used in both
World Wars. Submarines were also used for inserting and removing
covert agents and military forces, for intelligence-gathering and
to rescue aircrew during large-scale air attacks on islands, where
the airmen would be told of safe places to crash-land damaged
aircraft so the submarine crew could rescue them. Submarines could
carry cargo through hostile waters or act as supply vessels for
other submarines.

Submarines
could usually locate and attack other submarines only on the
surface, although managed to sink U-864 with a four torpedo spread while both were
submerged. The British developed a specialized
anti-submarine submarine in World War I, the R class. After World War II, with
the development of the homing torpedo, better sonar systems, and nuclear
propulsion, submarines also became able to hunt each other
effectively.

The primary defense of a submarine lies in its ability to remain
concealed in the depths of the ocean. Early submarines could be
detected underwater by the sound they made. Water is an excellent
conductor of sound, and submarines can detect and track
comparatively noisy surface ships from long distances. Modern
submarines are built with an emphasis on stealth. Advanced
propeller designs, extensive sound-reducing insulation, and special
machinery allow a submarine to be as quiet as ambient ocean noise,
making them extremely difficult to detect. It takes specialized
technology to find and attack modern submarines.

Active sonar uses the reflection of a sound emitted from the search
equipment to detect submarines. It has been used since World War II
by surface ships, submarines or even aircraft, but it gives away
the position of the emitter and is susceptible to
counter-measures.

A concealed military submarine is a real threat and, because of its
stealth, it can force an enemy navy to waste resources searching
large areas of ocean and protecting all ships against possible
attack. This advantage was vividly demonstrated in the 1982
Falklands War when the British
SSNHMS Conqueror sank the
Argentine cruiser General
Belgrano. After the sinking the Argentine Navy recognised
that they had no effective defense against submarine attack, and
the Argentine surface fleet withdrew to port for the remainder of
the war, though an Argentine submarine remained at sea.

Civil uses

Although the majority of the world's submarines are military ones,
there are some civil submarines. They have a variety of uses,
including tourism, exploration, oil and gas platform inspections
and pipeline surveys. The first tourist submarine was launched in
1985, and by 1997 there were 45 of them operating around the
world.

A semi-civilian use was the adaption of U-boats for cargo transport during World War I and
World War II.

Technology

Submersion and trimming

Control surfaces

All surface ships, as well as surfaced submarines, are in a
positively buoyant condition, weighing less
than the volume of water they would displace if fully submerged. To
submerge hydrostatically, a ship must have negative buoyancy,
either by increasing its own weight or decreasing its displacement
of water. To control their weight, submarines have ballast tanks, which can be filled with
outside water or pressurized air.

For general submersion or surfacing, submarines use the forward and
aft tanks, called Main Ballast Tanks or MBTs, which are filled with
water to submerge, or filled with air to surface. Under submerged
conditions, MBTs generally remain flooded, which simplifies their
design, and on many submarines these tanks are a section of
interhull space. For more precise and quick control of depth,
submarines use smaller Depth Control Tanks or DCTs, also called
hard tanks due to their ability to withstand higher pressure. The
amount of water in depth control tanks can be controlled either to
reflect changes in outside conditions or change depth. Depth
control tanks can be located either near the submarine's center of gravity, or separated along the
submarine body to prevent affecting trim.

When
submerged, the water pressure on submarine's hull can reach for
steel submarines and up to for titanium submarines like Komsomolets, while interior pressure remains relatively
unchanged. This difference results in hull compression,
which decreases displacement. Water density also increases with
depth, as the salinity and pressure are
higher, but this incompletely compensates for hull compression, so
buoyancy decreases as depth increases. A submerged submarine is in
an unstable equilibrium, having a tendency to either fall or float
to the surface. Keeping a constant depth requires continual
operation of either the depth control tanks or control
surfaces.

Submarines in a neutral buoyancy condition are not intrinsically
trim-stable. To maintain desired trim, submarines use forward and
aft trim tanks. Pumps can move water between these, changing weight
distribution, creating a moment pointing the sub up or down. A
similar system is sometimes used to maintain stability.

The hydrostatic effect of variable ballast tanks is not the only
way to control the submarine underwater. Hydrodynamic maneuvering
is done by several surfaces, which can be moved to create
hydrodynamic forces when a submarine moves at sufficient speed. The
stern planes, located near the propeller and normally horizontal,
serve the same purpose as the trim tanks, controlling the trim, and
are commonly used, while other control surfaces may not be present
on many submarines. The fairwater planes on the sail and/or bow
planes on the main body, both also horizontal, are closer to the
centre of gravity, and are used to control depth with less effect
on the trim.

When a submarine performs an emergency surfacing, all depth and
trim methods are used simultaneously, together with propelling the
boat upwards. Such surfacing is very quick, so the sub may even
partially jump out of the water, potentially damaging submarine
systems.

Submarine hull

Overview

Modern submarines are cigar-shaped. This design, visible in early
submarines (see below) is sometimes called a "teardrop hull". It reduces the hydrodynamic
drag when submerged, but decreases
the sea-keeping capabilities and increases drag while surfaced.
Since the limitations of the propulsion systems of early submarines
forced them to operate surfaced most of the time, their hull
designs were a compromise. Because of the slow submerged speeds of
those subs, usually well below 10 kt (18 km/h), the increased drag for
underwater travel was acceptable. Late in World War II, when
technology allowed faster and longer submerged operation and
increased aircraft surveillance forced submarines to stay
submerged, hull designs became teardrop shaped again to reduce drag
and noise. On modern military submarines the outer hull is covered
with a layer of sound-absorbing rubber, or anechoic plating, to reduce detection.

The occupied pressure hulls of deep diving submarines such as
DSV Alvin are spherical instead
of cylindrical. This allows a more even distribution of stress at
the great depth. A titanium frame is usually affixed to the
pressure hull, providing attachment for ballast and trim systems,
scientific instrumentation, battery packs, syntactic flotation foam, and lighting.

A raised tower on top of a submarine accommodates the periscope and electronics masts, which can include
radio, radar, electronic warfare, and other systems
including the snorkel mast. In many early classes of submarines
(see history), the control room, or "conn", was located inside this
tower, which was known as the "conning
tower". Since then, the conn has been located within the hull
of the submarine, and the tower is now called the "sail". The conn
is distinct from the "bridge", a small open platform in the top of
the sail, used for observation during surface operation.

"Bathtubs" are related to conning towers but are used on smaller
submarines. The bathtub is a metal cylinder surrounding the hatch
that prevents waves from breaking directly into the cabin. It is
needed because surfaced submarines have limited freeboard, that is, they lie low in the
water. Bathtubs help prevent swamping the vessel.

Single/double hull

Modern submarines and submersibles, as well as the oldest ones,
usually have a single hull. Large submarines generally have an
additional hull or hull sections outside. This external hull, which
actually forms the shape of submarine, is called the outer hull
(casing in the Royal Navy) or light hull,
as it does not have to withstand a pressure difference. Inside the
outer hull there is a strong hull, or pressure hull, which withstands sea pressure
and has normal atmospheric pressure inside.

As early as World War I, it was realized that the optimal shape for
withstanding pressure conflicted with the optimal shape for
seakeeping and minimal drag, and construction difficulties further
complicated the problem. This was solved either by a compromise
shape, or by using two hulls; internal for holding pressure, and
external for optimal shape. Until the end of World War II, most
submarines had an additional partial cover on the top, bow and
stern, built of thinner metal, which was flooded when submerged.
Germany went further with the Type XXI, the
general predecessor of modern submarines, in which the pressure
hull was fully enclosed inside the light hull, but optimized for
submerged navigation, unlike earlier designs that were optimized
for surface operation.

After World War II, approaches split. The Soviet Union changed its
designs, basing them on German developments. All post-World War II
heavy Soviet and Russian submarines are built with a double hull structure. American and most other
Western submarines switched to a primarily single-hull approach.
They still have light hull sections in the bow and stern, which
house main ballast tanks and provide a hydrodynamically optimized
shape, but the main cylindrical hull section has only a single
plating layer. The double hulls are being considered for future
submarines in the United States to improve payload capacity,
stealth and range.

Pressure hull

The pressure hull is generally constructed of thick high strength
steel with a complex structure and high strength reserve, and is
separated with watertight bulkheads into several compartments. There
are also examples of more than two hulls in a submarine, like the
Typhoon class, which has two
main pressure hulls and three smaller ones for control room,
torpedoes and steering gear, with the missile launch system between
the main hulls.

The dive depth cannot be
increased easily. Simply making the hull thicker increases the
weight and requires reduction of onboard equipment weight,
ultimately resulting in a bathyscaphe. This is acceptable for
civilian research submersibles, but not military submarines.

World War I submarines had hulls of carbon
steel, with a maximum depth. During World War II, high-strength
alloyed steel was introduced, allowing depths.
High-strength alloy steel remains the primary material for
submarines today, with depths, which cannot be exceeded on a
military submarine without design compromises. To exceed that
limit, a few submarines were built with titanium hulls. Titanium can be stronger than
steel, lighter, and is not ferromagnetic, important for stealth.
Titanium submarines were built by the Soviet Union, which developed
specialized high-strength alloys. It has produced several types of
titanium submarines. Titanium alloys allow a major increase in
depth, but other systems need to be redesigned to cope, so test
depth was limited to for the Soviet
submarine Komsomolets, the deepest-diving combat submarine. An
Alfa-class submarine may have
successfully operated at , though continuous operation at such
depths would produce excessive stress on many submarine systems.
Titanium does not flex as readily as steel, and may become brittle
during many dive cycles. Despite its benefits, the high cost of
titanium construction led to the abandonment of titanium submarine
construction as the Cold War ended. Deep diving civilian submarines
have used thick acrylic pressure
hulls.

The
deepest deep diving
submarine to date is Trieste[4943]departed San Diego on October 5, 1959 for
Guam aboard the freighter Santa Maria to
participate in Project
Nekton, a series of very deep dives in the Mariana Trench.On January 23, 1960, Trieste
reached the ocean floor in the Challenger Deep (the deepest
southern part of the Mariana Trench), carrying Jacques Piccard (son of Auguste) and
Lieutenant Don Walsh, USN. This was the
first time a vessel, manned or unmanned, had reached the deepest
point in the Earth's oceans. The onboard systems indicated a depth
of , although this was later revised to and more accurate
measurements made in 1995 have found the Challenger Deep to be
slightly shallower, at .

The task of building a pressure hull is very difficult, as it must
withstand pressures up to that of its required diving depth. When
the hull is perfectly round in cross-section, the pressure is
evenly distributed, and causes only hull compression. If the shape
is not perfect, the hull is bent, with several points heavily
strained. Inevitable minor deviations are resisted by stiffener
rings, but even a one inch (25 mm) deviation from roundness
results in over 30 percent decrease of maximal hydrostatic load and
consequently dive depth. The hull must therefore be constructed
with high precision. All hull parts must be welded without defects,
and all joints are checked multiple times with different methods,
contributing to the high cost of modern submarines. (For example,
each Virginia-class
attack submarine costs US$2.6 billion, over US$200,000 per ton of displacement.)

Propulsion

Originally, submarines were human propelled. The first mechanically
driven submarine was the 1863 French Plongeur, which used
compressed air for propulsion. Anaerobic propulsion was first
employed by the Spanish Ictineo II
in 1864, which used a solution of zinc,
manganese dioxide, and potassium chlorate to generate sufficient
heat to power a steam engine, while also providing oxygen for the crew. A similar system was not
employed again until 1940 when the German Navy tested a hydrogen peroxide-based system, the
Walterturbine, on the experimental V-80 submarine and later on the naval
U-791 and type XVII submarines.

Until the advent of nuclear
marine propulsion, most 20th century submarines used batteries
for running underwater and gasoline
(petrol) or diesel engines on the
surface, and for battery recharging. Early submarines used
gasoline, but this quickly gave way to kerosene , then diesel, because of reduced
flammability. Diesel-electric became the standard means of
propulsion. The diesel or gasoline engine and the electric motor,
separated by clutches, were initially on the same shaft driving the
propeller. This allowed the engine to drive the electric motor as a
generator to recharge the batteries and also propel the submarine.
The clutch between the motor and the engine would be disengaged
when the submarine dove, so that the motor could drive the
propeller. The motor could have multiple armatures on the shaft,
which could be electrically coupled in series for slow speed and in
parallel for high speed. (These connections were called "group
down" and "group up", respectively.)

Electric transmission

Diesel-electric

Early submarines used a direct mechanical connection between the
engine and propeller, switching between diesel engines for surface
running, and electric motors for submerged propulsion.

In 1928 the United States Navy's
Bureau of Engineering proposed a diesel-electric transmission;
instead of driving the propeller directly while running on the
surface, the submarine's diesel would drive a generator which could
either charge the submarine's batteries or drive the electric
motor. This meant that motor speed was independent of the diesel
engine's speed, and the diesel could run at an optimum and
non-critical speed, while one or more of the diesel engines could
be shut down for maintenance while the submarine continued to run
using battery power. The concept was pioneered in 1929 in the
S-class submarinesS-3, S-6, and S-7 to test the concept. No other
navy adopted the system before 1945, apart from the Royal Navy's
U-class submarines, though
some submarines of the Imperial Japanese Navy used separate diesel
generators for low speed running.

Other advantages of such an arrangement were that a submarine could
travel slowly with the engines at full power to recharge the
batteries quickly, reducing time on the surface or on snorkel. It was then possible to insulate the noisy diesel engines from the
pressure hull, making the submarine quieter. Additionally,
diesel-electric transmissions were more compact.

Air-independent propulsion

During the Second World War, German Type XXI submarines were
designed to carry hydrogen peroxide for long-term, fast
air-independent propulsion, but were ultimately built with very
large batteries instead. At the end of the War, the British and Russians experimented with hydrogen
peroxide/kerosene (paraffin) engines which could be used surfaced
and submerged. The results were not encouraging; although
the Russians deployed a class of submarines with this engine type
(codenamed Quebec by NATO),
they were considered unsuccessful.

Nuclear power

Steam power was resurrected in the 1950s with a nuclear-powered
steam turbine driving a generator. By eliminating the need for
atmospheric oxygen, the length of time that a modern submarine
could remain submerged was limited only by its food stores, as
breathing air was recycled and fresh water distilled from seawater. Nuclear-powered
submarines have a relatively small battery and diesel
engine/generator powerplant for emergency use if the reactors must
be shut down.

Nuclear power is now used in all large submarines, but due to the
high cost and large size of nuclear reactors, smaller submarines
still use diesel-electric propulsion. The ratio of larger to
smaller submarines depends on strategic needs. The US Navy,
French Navy, and the Royal Navy operate only nuclear submarines, which
is explained by the need for distant operations. Other major
operators rely on a mix of nuclear submarines for strategic
purposes and diesel-electric submarines for defence. Most fleets
have no nuclear submarines, due to the limited availability of
nuclear power and submarine technology.

Diesel-electric submarines have a stealth advantage over their
nuclear counterparts. Nuclear submarines generate noise from
coolant pumps and turbo-machinery needed to operate the reactor,
even at low power levels. Some nuclear submarines such as the
American Ohio class do
not have coolant pumps, etc. in the reactors, and are quieter than
electric subs. A conventional submarine operating on batteries is
almost completely silent, the only noise coming from the shaft
bearings, propeller, and flow noise around the hull, all of which
stops when the sub hovers in mid water to listen. Commercial
submarines usually rely only on batteries, since they never operate
independently of a mother ship.

Alternative propulsion

Oil-fired steam turbines powered the British K-class submarines, built during
the first World War (and later), to give
them the surface speed to keep up with battle fleet. The K-class
subs were not very successful, however.

Toward the end of the 20th century, some submarines, such as the
British Vanguard class, began to be fitted with pump-jet propulsors instead of propellers. Although
these are heavier, more expensive, and less efficient than a
propeller, they are significantly quieter, giving an important
tactical advantage.

Magnetohydrodynamic drive
(MHD) was portrayed as the operating principle behind the titular
submarine's nearly silent propulsion system in the film adaptation of
The Hunt for Red
October. However, in the novel, the Red October
did not use MHD. Although experimental surface ships have used this
system, speeds have been below expectations. In addition, the drive
system can induce bubble formation, compromising stealth, and the
low efficiency requires high powered reactors. These factors make
it unlikely for military usage.

Armament

The success of the submarine is inextricably linked to the
development of the torpedo, invented by
Robert Whitehead in 1866. His
invention is essentially the same now as it was 140 years ago. Only
with self propelled torpedoes could the submarine make the leap
from novelty to a weapon of war. Until the perfection of the
guided torpedo, multiple "straight
running" torpedoes were required to attack a target. With at most
20 to 25 torpedoes stored onboard, the number of attacks was
limited. To increase combat endurance most World War I submarines
functioned as submersible gunboats, using their deck guns against unarmed targets, and diving to
escape and engage enemy warships. The importance of guns encouraged
the development of the unsuccessful Submarine Cruiser such
as the French Surcouf and
the Royal Navy's X1 and M-class submarines. With the
arrival of ASW aircraft, guns
became more for defence than attack. A more practical method of
increasing combat endurance was the external torpedo tube, loaded
only in port.

The forward torpedo tubes in HMS
Ocelot

The ability of submarines to approach enemy harbours covertly led
to their use as minelayers. Minelaying
submarines of World War I and World War II were specially built for
that purpose. Modern submarine-laid mines, such as the British Mark 6 Sea Urchin, are
designed to be deployed by a submarine's torpedo tubes.

After World War II, both the US and the USSR experimented with
submarine launched cruise missiles
such as the SSM-N-8 Regulus and
P-5 Pyatyorka. Such missiles required
the submarine to surface to fire its missiles. They were the
forerunners of modern submarine launched cruise missiles, which can
be fired from the torpedo tubes of submerged submarines, for
example the US BGM-109 Tomahawk and
Russian RPK-2 Viyuga. Ballistic
missiles can also be fired from a submarine's torpedo tubes, for
example missiles such as the anti-submarine SUBROC, and versions of surface to surface anti-ship missiles such as the Exocet and Harpoon,
encapsulated for submarine launch. With internal volume as limited
as ever and the desire to carry heavier warloads, the idea of the
external launch tube was revived, usually for encapsulated
missiles, with such tubes being placed between the internal
pressure and outer streamlined hulls.

Germany is working on the short-range IDAS which is launched from a torpedo tube
and can be used against ASW helicopters as well as surface ships
and coastal targets.

Sensors

A submarine will have a variety of sensors determined by its
missions. Modern military submarines rely almost entirely on a
suite of passive and active sonars to find
their prey. Active sonar relies on an audible "ping" to generate
echoes to reveal objects around the submarine. Active systems are
rarely used, as doing so reveals the sub's presence. Passive sonar
is a set of sensitive hydrophones set into the hull or trailed in a
towed array, generally several hundred feet long. The towed array
is the mainstay of NATO submarine detection systems, as it reduces
the flow noise heard by operators. Hull mounted sonar is employed
to back up the towed array, and in confined waters where a towed
array could be fouled by obstacles.

Submarines also carry radar equipment for detection of surface
ships and aircraft. Sub captains are more likely to use radar
detection gear rather than active radar to detect targets, as radar
can be detected far beyond its own return range, revealing the
submarine. Periscopes are rarely used, except for position fixes
and to verify a contact's identity.

Civilian submarines, such as the DSV
Alvin or the Russian
Mir submersibles, rely on small active sonar sets and
viewing ports to navigate. Sunlight does not penetrate below about
underwater, so high intensity lights are used to illuminate the
viewing area.

Navigation

Early submarines had few navigation aids, but modern subs have a
variety of navigation systems. Modern military submarines use an
inertial guidance system
for navigation while submerged, but drift error unavoidably builds
up over time. To counter this, the Global Positioning System will
occasionally be used to obtain an accurate position. The periscope - a retractable tube with prism allowing a view to the surface - is
only used occasionally in modern submarines, since the range of
visibility is short. The Virginia-class submarines
and Astute-class
submarines have photonics masts
rather than hull-penetrating optical periscopes. These masts must
still be hoisted above the surface, and employ electronic sensors
for visible light, infrared, laser range-finding, and
electromagnetic surveillance.

Communication

Military submarines have several systems for communicating with
distant command centers or other ships. One is VLF radio, which can
reach a submarine either on the surface or submerged to a fairly
shallow depth, usually less than . ELF frequencies can reach a
submarine at much greater depths, but have a very low bandwidth and
are generally used to call a submerged sub to a shallower depth
where VLF signals can reach. A submarine also has the option of
floating a long, buoyant wire to a shallower depth, allowing VLF
transmissions to be made by a deeply submerged boat.

By extending a radio mast, a submarine can also use a "burst
transmission" technique. A burst transmission takes only a fraction
of a second, minimizing a submarine's risk of detection.

To communicate with other submarines, a system known as Gertrude is
used. Gertrude is basically a sonar telephone. Voice communication
from one submarine is transmitted by low power speakers into the
water, where it is detected by passive sonars on the receiving
submarine. The range of this system is probably very short, and
using it radiates sound into the water, which can be heard by the
enemy.

Civilian submarines can use similar, albeit less powerful systems
to communicate with support ships or other submersibles in the
area.

Command and control

All submarines need facilities to control their motion. Military
submarines also need facilities to operate their sensors and
weapons.

Crew

A typical nuclear submarine has a crew of over 80. Non-nuclear
boats typically have fewer than half as many. The conditions on a
submarine can be difficult because crew members must work in
isolation for long periods of time, without family contact.
Submarines normally maintain radio
silence to avoid detection. Operating a submarine is dangerous,
even in peacetime, and submarines have been lost in
accidents.

The British Royal Navy also does not permit women to serve on its
submarines because of "medical concerns for the safety of the
foetus and hence its mother" due to the potentially compromised air
quality onboard submarines.

Women have served on U.S.Navy surface ships since 1993 but do not serve on
submarines. The Navy only allows three exceptions for
women being on board military submarines: Female civilian
technicians for a few days at most; Women midshipmen on an overnight during summer training
for both Navy ROTC and Naval
Academy; Family members for one-day dependent
cruises.

Life support systems

With nuclear power, submarines can
remain submerged for months at a time. Diesel submarines must
periodically resurface or snorkel
to recharge their batteries. Most modern military submarines
generate breathing oxygen by electrolysis of water. Atmosphere control
equipment includes a CO2
scrubber, which uses an amine absorbent to
remove the gas from air and diffuse it into waste pumped overboard.
A machine that uses a catalyst to convert
carbon monoxide into carbon dioxide
(removed by the CO2 scrubber) and bonds hydrogen produced from the ship's storage battery
with oxygen in the atmosphere to produce water, is also used. An
atmosphere monitoring system samples the air from different areas
of the ship for nitrogen, oxygen, hydrogen,
R-12 and R-114 refrigerants, carbon
dioxide, carbon monoxide, and other
gases. Poisonous gases are removed, and oxygen is replenished by
use of an oxygen bank located in a main ballast tank. Some heavier
submarines have two oxygen bleed stations (forward and aft). The
oxygen in the air is sometimes kept a few percent less than
atmospheric concentration to reduce fire danger.

Fresh water is produced by either an evaporator or a reverse osmosis unit. The primary use for
fresh water is to provide feed water for the reactor and steam
propulsion plants. It is also available for showers, sinks, cooking
and cleaning once propulsion plant needs have been met. Seawater is
used to flush toilets, and the resulting "black water" is stored in a sanitary tank
until it is blown overboard using pressurized air or pumped
overboard by using a special sanitary pump. The method for blowing
sanitaries overboard is difficult to operate, and the German
Type VIIC boat U-1206 was lost with
casualties because of a mistake with the toilet. Water from showers
and sinks is stored separately in "gray
water" tanks, which are pumped overboard using the drain
pump.

Trash on modern large submarines is usually disposed of using a
tube called a Trash Disposal Unit (TDU), where it is compacted into
a galvanized steel can. At the bottom of the TDU is a large ball
valve. An ice plug is set on top of the ball valve to protect it,
the cans atop the ice plug. The top breech door is shut, and the
TDU is flooded and equalized with sea pressure, the ball valve is
opened and the cans fall out assisted by scrap iron weights in the
cans. The TDU is also flushed with seawater to ensure it is
completely empty and the ball valve is clear before shutting the
valve.

History of submarines

Early history of submarines and the first submersibles

The first submersible with reliable information on its construction
was built in 1620 by Cornelius
Jacobszoon Drebbel, a Dutchman in the service of James I of England. It was created to the
standards of the design outlined by English mathematician William Bourne. It was
propelled by means of oars. The precise nature of the submarine
type is a matter of some controversy; some claim that it was merely
a bell towed by a boat. Two improved types were tested in the
Thames between 1620 and 1624. In 2002 a two-person
version of Bourne's design was built for the BBC
TV programme Building the
Impossible by Mark
Edwards, and successfully rowed under water at Dorney Lake, Eton.

Though the first submersible vehicles were tools for exploring
under water, it did not take long for inventors to recognize their
military potential. The strategic advantages of submarines were
set out by Bishop John Wilkins of
Chester, England, in Mathematicall Magick in
1648:

Tis private: a man may thus go to any coast in the world
invisibly, without discovery or prevented in his journey.

Tis safe, from the uncertainty of Tides, and the violence of
Tempests, which do never move the sea above five or six paces deep.
From Pirates and Robbers which do so infest other voyages; from ice
and great frost, which do so much endanger the passages towards the
Poles.

It may be of great advantages against a Navy of enemies, who by
this may be undermined in the water and blown up.

It may be of special use for the relief of any place besieged
by water, to convey unto them invisible supplies; and so likewise
for the surprisal of any place that is accessible by water.

It may be of unspeakable benefit for submarine
experiments.

The first military submarines

The first military submarine was Turtle (1775), a hand-powered
egg-shaped device designed by the American David Bushnell to accommodate a single
person. It was the first verified submarine capable of independent
underwater operation and movement, and the first to use screws
for propulsion. During the American Revolutionary War,
Turtle (operated by Sgt. Ezra Lee, Continental Army) tried and
failed to sink the British warship HMS
Eagle, flagship of the blockaders in New York harbor on September 7, 1776.

In 1800, France built a human-powered submarine designed by
American Robert Fulton, the Nautilus. The French eventually
gave up on the experiment in 1804, as did the British when they
later considered Fulton's submarine design.

During
the War of 1812, in 1814, Silas Halsey
lost his life while using a submarine in an unsuccessful attack on
a British warship stationed in New London harbor.

In 1851,
a Bavarian artillery corporal, Wilhelm
Bauer, took a submarine designed by him called the Brandtaucher
(incendiary-diver) to sea in Kiel
Harbour. This submarine was built by August Howaldt and powered by a treadwheel. It sank but the three crew managed to
escape. The submarine was raised in 1887 and is on display in a
museum in Dresden.

Submarines in the American Civil War

During the American Civil War,
the Union was the first to field a submarine. The French-designed
Alligator was the first
U.S.Navy sub and
the first to feature compressed air (for air supply) and an air
filtration system. Initially hand-powered by oars, it was converted
after 6 months to a screw propeller powered by a hand crank. With a
crew of 20, it was larger than Confederate submarines.
Alligator was 47 feet (14.3 m) long and about 4 feet (1.2
m) in diameter. It was lost in a storm off Cape Hatteras on April 1, 1863 with no crew and under tow to its
first combat deployment at Charleston.

The Confederate submarine H.L.Hunley (named for one of
its financiers, Horace Lawson
Hunley) was intended for attacking the North's ships, which
were blockading the South's seaports. The submarine had a long pole
with an explosive charge in the bow, called a spar torpedo. The sub had to approach an enemy
vessel, attach an explosive, move away, and then detonate it. The
sub was extremely hazardous to operate, and had no air supply other
than what was contained inside the main compartment. On two
occasions, the sub sank; on the first occasion half the crew died
and on the second, the entire eight-man crew (including Hunley
himself) drowned. On February 17, 1864 Hunley sank
USS Housatonic off
Charleston Harbor, the first time a submarine successfully sank
another ship, though it sank in the same engagement shortly after
signaling its success. Submarines did not have a major impact on
the outcome of the war, but did portend their coming importance to
naval warfare and increased interest in their use in naval
warfare.

South America

The first
submarine in South America was the Hipopotamo, tested in
Ecuador on September 18, 1837.It was built by Jose
Rodriguez Lavandera, who successfully crossed the Guayas River in Guayaquil accompanied by Jose Quevedo. Rodriguez
Lavandera enrolled in the Navy in 1823, becoming a Lieutenant by
1830. The Hipopotamo crossed the Guayas on two more
occasions, but it was then abandoned because of lack of funding and
interest from the government.

The
submarine Flach was
commissioned in 1865 by the Chilean government during the war of
Chile and Peru against
Spain (1864-1866). It was built by the German
engineer Karl Flach. The submarine sank during tests in Valparaiso bay on May 3, 1866, with the entire eleven-man
crew.

Mechanically-powered submarines (late 19th century)

The first submarine not relying on human power for propulsion was
the French Plongeur, launched in 1863,
and using compressed air at 180 psi (1241 kPa).

The first combustion-powered submarine was Ictineo II, designed in Spain by Narcís Monturiol. Originally
launched in 1864 as human-powered, propelled by 16 , it was
converted to peroxide propulsion and steam in 1867. The
14 meter (46 ft) craft was designed for a crew of two,
could dive to 30 metres (96 ft), and demonstrated dives
of two hours. On the surface it ran on a steam engine, but
underwater such an engine would quickly consume the submarine's
oxygen; so Monturiol invented an air-independent propulsion
system. While the air-independent power system drove the screw,
the chemical process driving it also released oxygen into the hull
for the crew and an auxiliary steam engine. Monturiol's fully
functional, double hulled vessels also solved pressure and buoyancy
control problems that had bedeviled earlier designs.

In 1879, the Peruvian government, during the War of the Pacific, commissioned and
built the fully operational submarine Toro Submarino. It never saw military
action before being scuttled after the defeat of that country in
the war to prevent its capture by the enemy.

The first submarine to be mass-produced was human-powered. It was
the submarine of the Polish inventor Stefan Drzewiecki—50 units were built
in 1881 for the Russian government. In 1884 the same inventor built
an electric-powered submarine.

Discussions between the English clergyman and inventor George Garrett and the industrially and
commercially adept Swede Thorsten
Nordenfelt led to a series of steam-powered submarines.
The first
was the Nordenfelt I, a 56 tonne, 19.5 metre
(64 ft) vessel similar to Garret's ill-fated Resurgam (1879), with a range of 240 kilometres
(150 mi, 130 nm), armed with a single torpedo, in 1885. Like Resurgam,
Nordenfelt I operated on the surface by steam, then shut
down its engine to dive. While submerged the submarine released
pressure generated when the engine was running on the surface to
provide propulsion for some distance underwater. Greece, fearful of
the return of the Ottomans, purchased
it. Nordenfelt then built Nordenfelt II
(Abdülhamid) in 1886 and Nordenfelt III
(Abdülmecid) in 1887, a pair of 30 metre
(100 ft) submarines with twin torpedo
tubes, for the Ottoman navy. Abdülhamid became the
first submarine in history to fire a torpedo submerged.
Nordenfelt's efforts culminated in 1887 with Nordenfelt IV
which had twin motors and twin torpedoes. It was sold to the
Russians, but proved unstable, ran aground, and was scrapped.

On September 8, 1888, an electrically powered vessel built by the
Spanish engineer and sailor Isaac Peral
for the Spanish Navy was launched. It
had two torpedoes, new air systems, and a hull shape, propeller,
and cruciform external controls anticipating much later designs.
Its underwater speed was ten knots (19 km/h). In June
1890 Peral's submarine launched a torpedo while submerged. Its
ability to fire torpedoes under water while maintaining full
propulsive power and control has led some to call it the first
U-boat. After many successful dives the
project was scrapped because of the difficulties of recharging at
sea and the short range of battery-powered vessels.

Shortly after, the French Gymnote was launched on
September 24, 1888. The electrically-powered Gymnote,
another fully functional military submarine, completed
2,000 dives successfully.

Many more designs were built at this time by various inventors, but
submarines were not to become effective weapons until the 20th
century.

Late 19th century to World War I

USS Plunger, launched in 1902

The turn of the 19th century marked a pivotal time in the
development of submarines, with a number of important technologies
making their debut, as well as the widespread adoption and fielding
of submarines by a number of nations. Diesel electric propulsion
would become the dominant power system and equipment such as the
periscope would become standardized. Large numbers of experiments
were done by countries on effective tactics and weapons for
submarines, all of which would culminate in them making a large
impact on the coming World War I.

A prototype version of the Plunger-class or A-class
submarines, the Fulton, was developed at Nixon's Crescent
Shipyard for the United States Navy before the construction of the
A-class submarines there in 1901. A naval
architect and shipbuilder from the United Kingdom, Arthur Leopold
Busch, superintended the development of these first submarines
for Holland's company. However the Fulton was never
purchased by the U.S. Navy and was eventually sold to the Imperial Russian Navy during the
Russo-Japanese War of 1904-1905.
Two other
A-class vessels were built on the West Coast of (USA) at Mare Island
Naval Shipyard/Union
Iron Works circa 1901. In 1902, Holland received a
patent for his persistent pursuit to perfect the underwater naval
craft. By this time, Holland was no longer in control of the
day-to-day operations at Electric Boat, as others were now at the
helm of the company he once founded. The acumen of business were
now in control of these operations as Holland was forced to step
down. His resignation from the company was to be effective as of
April 1904.

Commissioned in June 1900, the French steam and electric submarine
Narval introduced the classic double-hull design, with a
pressure hull inside the outer light hull. These 200-ton ships had
a range of over on the surface, and over underwater. The French
submarine Aigrette in 1904 further improved the concept by
using a diesel rather than a gasoline engine for surface power.
Large numbers of these submarines were built, with seventy-six
completed before 1914.

The U-boats' ability to function as practical war machines relied
on new tactics, their numbers, and submarine technologies such as
combination diesel-electric power system developed in the preceding
years. More submersibles than true submarines, U-boats operated
primarily on the surface using regular engines, submerging
occasionally to attack under battery power. They were roughly
triangular in cross-section, with a distinct keel to control rolling while surfaced, and a distinct
bow.

Interwar developments

Various new submarine designs were developed during the interwar
years. Among the most notorious ones were submarine aircraft carriers,
equipped with a waterproof hangar and steam catapult to launch and
recover one or more small seaplanes. The submarine and its plane
could then act as a reconnaissance unit ahead of the fleet, an
essential role at a time when radar still did
not exist. The first example was the British HMS M2, followed by the French Surcouf, and
numerous aircraft-carrying submarines in the Imperial Japanese
Navy.

Submarines during World War II

Germany

Germany had the largest submarine fleet during World War II. Due to the Treaty of Versailles limiting the
surface navy, the rebuilding of the German surface forces had only
begun in earnest a year before the outbreak of World War II.
Expecting to be able to defeat the Royal
Navy through underwater warfare, the German High Command
pursued commerce raiding and
immediately stopped all construction on capital surface ships save
the nearly completed Bismarck-class battleship
and two cruisers, switching its resources to submarines, which
could be built more quickly. Though it took most of 1940 to expand
the production facilities and get the mass production started, more
than a thousand submarines were built by the end of the war.

Germany put submarines to devastating effect in the Second Battle of the Atlantic
in World War II, attempting but ultimately failing to cut off
Britain's supply routes by sinking more merchant ships than Britain could replace. The
supply lines were vital to Britain for food and industry, as well
as armaments from the US. Although the U-boats had been updated in
the intervening years, the major innovation was improved
communications, encrypted using the famous Enigma cipher machine. This allowed for
mass-attack tactics or "wolf packs" (Rudeltaktik), but was also ultimately
the U-boats' downfall.

After putting to sea, U-boats operated mostly on their own, trying
to find convoys in areas assigned to them by the High Command. If a
convoy was found, the submarine did not attack immediately, but
shadowed the convoy to allow other submarines in the area to find
the convoy. These were then grouped into a larger striking force to
attack the convoy simultaneously, preferably at night while
surfaced.

From September 1939 to the beginning of 1943, the
Ubootwaffe ("U-boat force") scored unprecedented success
with these tactics, but were too few to have any decisive success.
By the spring of 1943, German U-boat construction was at full
capacity, but this was more than nullified by increased numbers of
convoy escorts and aircraft, as well as technical advances like
radar and sonar. Huff-Duff and Ultra allowed
the Allies to route convoys around wolf packs when they detected
them from their radio transmissions. The results were devastating:
from March to July of that year, over 130 U-boats were lost,
41 in May alone. Concurrent Allied losses dropped dramatically,
from 750,000 tons in March to only 188,000 in July.
Although
the Second battle of the
Atlantic would continue to the last day of the war, the U-boat
arm was unable to stem the tide of personnel and supplies, paving
the way for Operation
Torch, Operation Husky,
and ultimately, D-Day.Winston Churchill wrote that the U-boat
"peril" was the only thing that ever gave him cause to doubt the
Allies' eventual victory.

Japan

The Imperial Japanese Navy
started their submarine service with five Holland Type VII
submarines purchased from the Electric Boat Company in 1904. Japan
had the most varied fleet of submarines of World War II; including Kaiten crewed torpedoes, midget submarines
(Ko-hyoteki and
Kairyu),
medium-range submarines, purpose-built supply submarines and
long-range fleet submarines. They also had submarines with the
highest submerged speeds during World War II (I-200-class submarine) and
submarines that could carry multiple aircraft (I-400-class submarine). They
were also equipped with one of the most advanced torpedoes of the
conflict, the oxygen-propelled Type
95.

Nevertheless, despite their technical prowess, Japan had chosen to
utilize its submarines for fleet warfare, and consequently were
relatively unsuccessful, as warships were fast, maneuverable and
well-defended compared to merchant ships. In 1942, a Japanese
submarine sank one aircraft carrier, damaged one battleship, and
damaged one destroyer (which sank later) from one torpedo salvo;
and during the Battle of
Midway were able to deliver the coup de grace to another fleet aircraft
carrier. With the lack of fuel oil and air supremacy,
Imperial submarines were not able to sustain those kind of results
afterwards. By the end of the war, submarines were instead often
used to transport supplies to island garrisons.

United States

The United States Navy used its submarine force to attack both
warships and merchant shipping; and destroyed more Japanese
shipping than all other weapons combined. This feat was
considerably aided by the Imperial Japanese Navy's failure to
provide adequate escort forces for the nation's merchant
fleet.

Whereas Japan had the finest submarine torpedoes of the war, the
U.S. Navy had the worst: the Mark 14
torpedo that ran ten feet too deep, tipped with a Mk VI
exploder that was based on an unimproved version of the Mark V
contact exploder but with an additional magnetic exploder, neither
of which was reliable. The faulty depth control mechanism of the
Mark 14 was corrected in August 1942, but field trials for the
exploders were not ordered until mid-1943, when tests in Hawaii and
Australia confirmed the flaws. Fully operational Mark 14 torpedoes
were not put into service until September 1943. The Mark 15 torpedo
used by US surface combatants had the same Mk VI exploder and was
not fixed until late 1943. One attempt to correct the problems
resulted in a wakeless, electric torpedo being placed in submarine
service, but USS Tang and
Tullibee were lost to
self-inflicted hits by these torpedoes.

During World War II, 314 submarines served in the United
States Navy, of which nearly 260 were deployed to the
Pacific.O'Kane, p. 333 On December 7, 1941, 111 boats were in
commission; 203 submarines from the Gato, Balao, and Tench classes were
commissioned during the war. During the war, 52 US submarines were
lost to all causes, with 48 lost directly to hostilities; 3,505
sailors were lost, the highest percentage killed in action of any US service arm in
World War II. US submarines sank 1,560 enemy vessels, a total
tonnage of 5.3 million tons, including 8 aircraft
carriers and over 200 warships.

United Kingdom

The Royal Navy Submarine
Service was primarily used to enforce the classic British
blockade role. It therefore chiefly
operated in inshore waters and tended to only surface by
night.

In the war British submarines sank 2 million tons of enemy
shipping and 57 major warships, the latter including
35 submarines. Amongst these is the only instance ever of a
submarine sinking another submarine while both were submerged.
This
occurred when HMS
Venturer engaged the U864; the Venturer crew
manually computed a successful firing solution against a
three-dimensionally manoeveuring target using techniques which
became the basis of modern torpedo computer targeting systems.
Seventy-four British submarines were lost, half probably to
naval mines.

The snorkel

The diesel engines on HMS
Ocelot charged the batteries located beneath the
decking.

Diesel-electric submarines need air to run their diesel engines,
and so carried very large batteries for submerged operation. The
need to recharge the batteries from the diesel engines limited the
endurance of the submarine while submerged and required it to
surface regularly for extended periods, during which it was
especially vulnerable to detection and attack. The snorkel, a pre-war Dutch invention, was
used to allow German submarines to run their diesel engines whilst
running just under the surface, drawing air through a tube from the
surface.

The German Navy also experimented with engines that would use
hydrogen peroxide to allow diesel
fuel to be used while submerged, but technical difficulties were
great. The Allies experimented with a variety of detection systems,
including chemical sensors to "smell" the
exhaust of submarines.

Cold-war diesel-electric submarines, such as the Oberon class, used batteries
to power their electric motors in order to run silently. They
recharged the batteries using the diesel engines without ever
surfacing.

In the 1950s, nuclear power partially
replaced diesel-electric propulsion. Equipment was also developed
to extract oxygen from sea water.
These two
innovations gave submarines the ability to remain submerged for
weeks or months, and enabled previously impossible voyages such as
USS
Nautilus' crossing of the North pole beneath the Arctic ice cap in 1958 and the USS
Triton s submerged circumnavigation of the world in
1960. Most of the naval submarines built since that time in
the United States and the Soviet Union/Russia have been powered by
nuclear reactors. The limiting factors in submerged endurance for
these vessels are food supply and crew morale in the space-limited
submarine.

While the greater endurance and performance from nuclear reactors
makes nuclear submarines better for long-distance missions or the
protection of a carrier battle group, their reactor cooling pumps
have traditionally made them noisier, and thus easier to detect,
than conventional diesel-electric submarines. Diesel-electrics have
continued to be produced by both nuclear and non-nuclear powers as
they lack this limitation, except when required to run the diesel
engine to recharge the ship’s battery. Recent technological
advances in sound damping, noise isolation, and cancellation have
made nuclear subs quieter and substantially eroded this advantage.
Though far less capable regarding speed and weapons payload,
conventional submarines are also cheaper to build. The introduction
of air-independent
propulsion boats, conventional diesel-electric submarines with
some kind of auxiliary air-independent electricity generator, have
led to increased sales of such types of submarines.

During the Cold War, the United States and the Soviet Union
maintained large submarine fleets that engaged in cat-and-mouse
games. The Soviet Union suffered the loss of at
least four submarines during this period: K-129 was lost in 1968 (which the CIA
attempted to retrieve from the ocean floor with the Howard Hughes-designed ship Glomar Explorer), K-8 in 1970, K-219 in 1986, and Komsomolets in 1989 (which held a depth record among military
submarines—1000 m). Many other Soviet subs, such as
K-19 (the first
Soviet nuclear submarine, and the first Soviet sub to reach the
North Pole) were badly damaged by fire or radiation leaks.
The US
lost two nuclear submarines during this time: USS
Thresher due to equipment failure during a test dive while
at its operational limit, and USS
Scorpion due to unknown causes.

More recently, Russia has had three high profile submarine
accidents. The Kurskwent down with all hands
in 2000; the K-159 sank while being towed to a scrapyard in 2003, with
nine lives lost; and the Nerpa had an accident with
the fire-extinguishing system resulting in twenty deaths in late
2008.

Indian Prime MinisterManmohan Singh launched India's first
locally built nuclear-powered submarine, the Arihant, on
July 26, 2009."Today, we join a select group of five
nations who possess the capability to build a nuclear-powered
submarine," Singh stated during a speech at Visakhapatnam naval base.

Modern tourist submarines

Submarines with a crush depth in the range of are operated in
several areas worldwide, typically with bottom depths around , with
a carrying capacity of 50 to 100 passengers. In a typical operation
(for example, Atlantis
submarines), a surface vessel carries passengers to an offshore
operating area, where passengers are exchanged with those of the
submarine. The submarine then visits underwater points of
interests, typically either natural or artificial reef structures.
To surface safely without danger of collision the location of the
submarine is marked with an air release and movement to the surface
is coordinated by an observer in a support craft, this as described
to the occupants during operations.